The rate of installation of air bags on automobiles has been increasing in recent years, and air bag systems are becoming part of standard equipment regardless of vehicle types. It has been reported, however, that the air bags may become a cause of fatal accidents in the case where a child is standing in front of a seat, or a small woman is sitting in a seat, for example. Thus, various methods for controlling inflation of an air bag have been proposed in an attempt to avoid such fatal accidents. Among these methods, an embodiment shown in the above referenced parent application will be described below wherein a sensor is provided at a ceiling location in an automobile, for measuring distances from the sensor to an occupant, so as to detect the presence and posture of the occupant based on a distribution of the distances thus measured.
FIG. 21 is a schematic view for explaining the embodiment of the parent application, in which an occupant sensor 1, occupant 2, and an automobile 3 are illustrated.
In the example of FIG. 21, an image of the occupant 2 is formed by the occupant sensor 1, which defines four linear fields of view R1, R2, R3 and R4 with respect to the occupant 2, for example, and generates outputs representing a plurality of portions of the occupant located in the respective fields of view. A processing unit that is not illustrated processes the outputs of the occupant sensor 1, to measure distances from the sensor to the respective portions of the occupant and obtain a distance distribution for each field of view, thereby to determine not only the presence of the occupant but also his/her posture based on the distance distributions in the fields of view. The principle of distance measurement will be described later.
A variety of postures of occupants, or the like, may be determined by the above method. FIGS. 22-24 show the relationship among the vehicle seat, posture of an occupant, and fields of view of the sensor, and FIGS. 25-27 show results of distance measurements by the occupant sensor.
More specifically, FIG. 22(a) is a perspective view of a vehicle seat on which no occupant sits, FIG. 22(a)' is a side view corresponding to FIG. 22(a), FIG. 22(b) is a perspective view of a vehicle seat with an occupant who sits in a normal posture, FIG. 22(b)' is a side view corresponding to FIG. 22(b), FIG. 22(c) is a perspective view of a vehicle seat on which an occupant sits while leaning forward, and FIG. 22(c)' is a side view corresponding to FIG. 22(c). FIG. 23(a) is a perspective view showing a vehicle seat on which a child seat is mounted to face forward, along with a child sitting in the child seat, FIG. 23(a)' is a side view corresponding to FIG. 23 (a), FIG. 23(b) is a perspective view showing a vehicle seat on which a child seat is mounted to face backward, along with a child sitting in the child seat, FIG. 23(b)' is a side view corresponding to FIG. 23((b), FIG. 23(c) is a perspective view showing a vehicle seat and a child who is standing in front of the seat in a vehicle compartment, and FIG. 23(c)' is a side view corresponding to FIG. 23(c). FIG. 24 is a perspective view showing a vehicle seat with an occupant who sits sideways on the seat. A side view corresponding to FIG. 24 is similar to that of FIG. 22(b)' showing the occupant having the normal posture, and is therefore omitted herein.
FIG. 25(a), 25(b), 25(c) are examples of patterns of distance distributions obtained in the cases of FIG. 22(a), 22(b), 22(c), respectively, and FIG. 26(a), 26(b), 26(c) are examples of patterns of distance distributions obtained in the cases of FIG. 23(a), 23(b) and 23(c), respectively. FIG. 27(a) shows examples of patterns of distance distributions obtained in the case of FIG. 24, and FIG. 27(b) shows examples of patterns of distance distributions obtained in the case where a child seat facing forward is mounted on a vehicle seat with no child sitting in it. In the distance distribution charts of FIG. 25(a) through FIG. 27(b), the vertical axis represents distance from the sensor, and the horizontal axis represents position within the field of view. This also applies to other distance distribution charts that will follow unless specified otherwise.
It will be understood from the above charts that distances measured in each field of view R1, R2, R3, R4 are obtained as discrete values. The concept to obtain such discrete distance values to form a pattern of distance distribution will be described later.
The presence and posture of a vehicle occupant is normally determined through a so-called pattern matching, namely, by comparing the pattern of distance distribution obtained for each field of view in the above manner with model patterns. There are, however, a considerably wide variety of model patterns that vary depending upon the presence and posture of a vehicle occupant, and further upon the distance or inclination from a reference position of the vehicle seat, for example. This undesirably requires an enormous amount of processing time to compare the pattern of distance distribution in a certain field of view with all of these model patterns.